Pill millipedes are any members of two living (and one extinct) orders of , often grouped together into a single superorder, Oniscomorpha. The name Oniscomorpha refers to the millipedes' resemblance to certain woodlouse (Oniscidea), also called pillbugs or roly-polies. However, millipedes and woodlice are not closely related (belonging to the subphylum Myriapoda and Crustacean, respectively); rather, this is a case of convergent evolution.
Description
Pill millipedes are relatively short-bodied compared to most other millipedes, with only eleven to thirteen
,
and are capable of rolling into a ball (
volvation) when disturbed, as a defense against predators. This ability
evolution separately in each of the two orders, making it a case of convergent evolution, rather than homology. They can also exude a noxious liquid, which may be both
causticity and
toxin among other millipede taxa, but is not in pill millipedes——
Glomerida secretes a clear, odorless liquid from the midline of the back that contains toxic alkaloids and has a sedative effect to repel predators.
Sphaerotheriida don't even have such ability, they completely rely on their hard shell to defend against enemies.
Pill millipedes are
detritivore, feeding on decomposing plant matter, usually in
.
Orders
Glomerida
The order
Glomerida is predominantly found in the Northern Hemisphere and includes species such as
Glomeris marginata, the common European pill millipede. They have from eleven to twelve body segments, and possess dorsal
(openings of the repugnatorial glands) rather than the lateral ozopores found on many other millipedes.
[ Glomeridans reach maximum lengths of , and eyes, if present, are in a single row of ocelli.]
Sphaerotheriida
The order Sphaerotheriida is a Gondwana-distribution taxon, with around 350 species in southern Africa, Madagascar,[
]
Amynilyspedida
Oniscomorpha also includes the extinct order Amynilyspedida from the upper Carboniferous of North America and Europe.[Hoffman, R. L. 1969. Myriapoda, exclusive of Insecta. In Treatise on Invertebrate Paleontology, Pt. R, Arthropoda 4, ed. R.C. Moore, 2:R572–606. Geological Society of America, Inc., and The University of Kansas.] Amynilyspedida differs from the other Oniscomorph orders in having 14–15 segments.[
]
External links
